An example of technologies that perform non-destructive inspection of the state of a welded portion and the state of a weld defect of a joined area between plate-like structures, an object to be inspected, is an ultrasonic test technology. In an ultrasonic inspection apparatus which adopts the ultrasonic test technology, the ultrasonic waves are irradiated to the welded area of the object to be inspected, and then are reflected from the welded area of the object to be inspected as echoes of the ultrasonic wave. After the reflected echoes of the ultrasonic wave are performed an imaging process, the ultrasonic inspection apparatus displays the reflected echoes performed the imaging process as an ultrasonic wave image, on the display device. The non-destructive inspection a state of the welded area or the weld defect is performed and thereby the user visually determines whether a state of the welded area or the weld defect is sound or not based on the ultrasonic wave image of the welded area.
Specifically, as described in Japanese Unexamined Patent Application Publication No. 11-326287 (Patent Document 1), when a plate-like structure is the object to be inspected, and two plate-like structures are superposed and joined together by means of spot welding, by inspecting the states of the welded portion between the two plate-like structures and a weld defect using the ultrasonic inspection apparatus, in a non-destructive manner, it is possible to inspect whether a molten-solidified portion exists in the welded portion or not, and the presence or absence of the weld defect such as a blowhole, and the state of the weld defect.
Further, as the inspection accuracy of the three-dimensional ultrasonic inspection apparatus constantly improves (increases), the three-dimensional ultrasonic inspection apparatus becomes possible to accurately and quantitatively determinate the state such as the layer structure, the weld defect in the object to be inspected, the presence or absence of the void or the separation, or the likes, of the welded area with respect to the object to be inspected. For example, the three-dimensional ultrasonic inspection apparatus disclosed in Japanese Published Unexamined Patent Application (Patent Laid-Open) No. 2005-315582 (Patent Document 2) inspects the positional relationship of the welded portion with respect to the object to be inspected, correctly, accurately and quantitatively in three dimensions.